Rare peripheral T cells migrate to and persist in normal mouse thymus

Area of Science:

• Immunology
• T cell biology
• Lymphocyte trafficking

Background:

• T cell traffic between the thymus and peripheral lymphoid organs is traditionally viewed as unidirectional.
• The thymus is primarily known as a site for T cell development and positive/negative selection.

Purpose of the Study:

• To investigate the potential for peripheral T cells to enter the thymus.
• To characterize the phenotype and location of peripheral T cells within the thymus.

Main Methods:

• Utilized a lymphocyte transfer technique between Thy-1 congenic mice.
• Analyzed donor peripheral T cells in host thymuses at various time points (3 hours to 24 weeks).
• Assessed T cell immunophenotype (Ly-1, PNA, L3T4, Lyt-2) and MEL-14 expression.

Main Results:

• Demonstrated the entry of rare peripheral lymph node T cells into the normal mouse thymus.
• Donor T cells were primarily found in the thymic medulla as scattered single cells.
• These cells maintained a stable, mature immunophenotype and a minority expressed the MEL-14 homing receptor.

Conclusions:

• The thymic medulla exhibits characteristics of a peripheral lymphoid organ.
• The rate of recirculating T cell turnover in the thymic medulla is significantly lower than in peripheral lymphoid organs.
• Challenges the long-held view of unidirectional T cell traffic into the thymus.